above you has written that you transfer a lot of roms to the system.
Have you looked that you have not transfered a non compatible character in the romname?
for example
correct = 720 Degrees.extension
wrong=720°.extension
This maybe can make problems.

When you can access the recalbox-manager via ip, look into the logs.

EDIT: the example file 720°.extension can be show up as 720?.extension in gamelist or your romfolder